ESQL: Support exponential histograms in TS queries

[JonasKunz]

• Add an internal default merge_over_time aggregation and use it automatically in TS contexts for exponential histograms ESQL: Support exponential histograms in TS queries #138563 (review)
• Add support for first_over_time for exponential histograms ESQL: Implement first/last_over_time for exponential histograms #138639
• Add support for last_over_time for exponential histograms ESQL: Implement first/last_over_time for exponential histograms #138639
• Add tests for percentile_over_time for exponential histograms ESQL: Add tests for remaining _over_time aggs for exponential histograms #138725
• Add tests for avg_over_time for exponential histograms ESQL: Add tests for remaining _over_time aggs for exponential histograms #138725
• Add tests for sum_over_time for exponential histograms ESQL: Add tests for remaining _over_time aggs for exponential histograms #138725
• Add tests for min_over_time for exponential histograms ESQL: Add tests for remaining _over_time aggs for exponential histograms #138725
• Add tests for max_over_time for exponential histograms ESQL: Add tests for remaining _over_time aggs for exponential histograms #138725
• Add tests for present_over_time for exponential histograms ESQL: Add tests for remaining _over_time aggs for exponential histograms #138725
• Add tests for absent_over_time for exponential histograms ESQL: Add tests for remaining _over_time aggs for exponential histograms #138725

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)